.cnav{
    width: 20%;  
    background-color: #eee;
    margin-top: .1rem;
    overflow-y: auto;
    float: left;  
    top: .8rem;
    left: 0;
    height: 5rem;
    position: fixed;
}
.cnav::-webkit-scrollbar{
    width: 0;
}
.cnav .itemli{
   width: .75rem;
    height: .5rem;
    line-height: .5rem;
    text-align: center;
    color: dimgray;
    position: relative;
}
.content{
    margin-top:0;
    overflow-y: auto;
    position: relative;
    top: .8rem;
}
.cnav .red{
    color: red;
     font-weight: 700;
     background-color: #fff;
}
.red::after{
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    width: .02rem;
    height: .5rem;
    background-color: red;
}